Brake wire slack
Your trailer is going to swing a maximum of 90 degrees on each side of the ball. Measure from your TV electrical connector to the center of the ball. Measure from the center of the ball to where the cable is attached to the trailer tongue. Add them together. I'd want my cable to be minimum of that length plus 6-8 inches.
2012 Dodge C3500 DRW 4x4 Long Box, WeatherGuard 90 Gal transfer tank, B&W Companion Hitch
2012 Keystone Montana 3100RL, 520W Solar, 460AH batteries, Morningstar MPPT 45 CC, Bogart 2030RV monitor.